The present invention relates to plastic bobbins and more particularly to a plastic bobbin having a barrel that is solid for a substantial portion thereof with a minimum of stresses therein so as to insure that the bobbin maintains its desired shape and configuration during manufacture and use thereof.
The terms quill and bobbin are used interchangeably throughout this application since such are often used to mean the same thing in the textile industry. Plastic quills or bobbins have been manufactured prior hereto but have not generally been commercially successful in the United States. One problem encountered in manufacturing plastic bobbins heretofore is that stresses often develop in the barrel of the bobbin during molding which tend to distort the shape of the bobbin. Attempts have been made to overcome these problems encountered in molding plastic bobbins and one such attempt utilized an elongated mandrel that extended for substantially the entire length of the barrel in axial alignment with the mold cavity. The problem encountered in such a device is that during the molding process, the plastic tends to expand and contract during the heating and cooling stages. This often caused the elongated mandrel to deviate from the center axis of the mold producing an uneven wall thickness in the bobbin. In an attempt to overcome the above problem a mandrel was used which extended entirely through the mold. In this way, both ends of the mandrel could be secured preventing such from deviating from the longitudinal axis. However, this presented a problem in that it produced a bobbin having an axial bore through the entire length of the barrel reducing the strength of the barrel.
The exterior dimension of a bobbin is generally dictated by the particular shuttle or apparatus in which such is being utilized. Accordingly, bobbin manufacturers have very little latitude in changing the exterior dimension and shape of the bobbin. The bobbin constructed in accordance with the present invention, accordingly, has the same exterior shape as conventional wooden bobbins and/or plastic bobbins now being utilized. Examples of plastic bobbins are disclosed in U.S. Pat. Nos. 2,605,979 granted to Gartrell on Aug. 5, 1952, 2,967,026 granted to Deventer, III, on Jan. 3, 1961 and 3,190,580 granted to Guerin, et al on June 22, 1965. As can be seen, each of these plastic bobbins has a hollow core extending through the barrel thereof minimizing the strength thereof. U.S. Pat. No. 3,268,636 granted to Angell, Jr. on Aug. 23, 1966, discloses a method and apparatus for injection molding foam plastic articles. As is disclosed, a blowing agent is mixed with a thermoplastic material to produce articles such as bowling pins and the like. Similarly, U.S. Pat. No. 3,776,989, granted to Annis, Jr., et al on Dec. 4, 1973, discloses another method for injection molding articles of foam material utilizing a screw extruder.